1. Field of the Invention
The present invention relates to a process and a catalyst for the production of diaryl carbonates, and more particularly to a process and a homogeneous catalyst for the homogeneous liquid phase reaction of aromatic haloformates with aromatic hydroxy compounds for the production of diaryl carbonates with the elimination of anhydrous hydrogen halide.
2. Description of the Related Art
Prior art methods for the production of diaryl carbonates have used the interfacial route involving a two phase reaction system, and various homogeneous catalytic systems. The interfacial route involves the neutralization of the aromatic hydroxy compound with caustic and the subsequent reaction of an aqueous solution of the phenate type salt of the aromatic hydroxy compound with a carbonyl halide, usually phosgene. In the case where the desired product is diphenyl carbonate, excess caustic to insure the complete neutralization of phenol results in a loss of about 20 percent of the phosgene. Salt which represents the loss of two chlor/alkali equivalents is produced. As a consequence, the aqueous stream coming from this reaction process requires treatment prior to disposal. Caustic equivalents include the Group 1, 2, 11 and 12 hydroxides, oxides, carbonates and phosphates.
The prior art alternatives to the above described interfacial route to diaryl carbonates are various homogeneous catalytic processes. U.S. Pat. No. 2,362,865 discloses the use of metal phenates as catalysts in the reaction of phenol and phosgene to form diphenyl carbonate in a process in which the phenol is in the liquid phase. U.S. Pat. Nos. 3,234,261 and 3,234,263 relate to the formation of diaryl carbonates from various chloroformates by reaction with metal oxides, with the process of the '263 patent employing a tertiary amine base as a catalyst. Related processes are disclosed in French Patent No. 1,361,228 and U.S. Pat. No. 3,251,873. U.S. Pat. No. 4,366,102 discloses a process which employs various organic phosphorous compounds as catalysts for the reaction of a phenol and phosgene to form an aromatic chloroformic ester.
A process for the reaction of aromatic hydroxy compounds with carbonyl halides to produce diaryl carbonates which employs a heterogeneous catalyst system is described in U.S. patent application Ser. No. 429,954 filed on Oct. 26, 1989, by Harley et al.
The use of organophosphines as catalysts for the reaction of an aromatic haloformate with an aromatic hydroxy compound which is carried out in an inert reaction medium is describe in U.S. patent application Ser. No. 451,894, filed of even date herewith, by Rand.
U.S. Pat. No. 3,170,946 discloses a process for the preparation of arylchloroformates using aromatic amine catalysts, and U.S. Pat. Nos. 3,211,774, 3,211,776 and 3,275,674 disclose processes for the preparation of aromatic esters of chloroformic acid using aromatic amine catalysts. U.S. Pat. No. 4,012,406 discloses a process for the preparation of diaryl carbonates by the reaction of aromatic monohydroxy compounds with phosgene with the aid of an aromatic heterocyclic basic nitrogen compound as a catalyst. Many such catalysts are effective for the conversion of haloformates and aromatic hydroxy compounds into diaryl carbonates, as would be expected, since a haloformate is an intermediate in the reaction of an aromatic hydroxy compound and phosgene to form the same product. The '406 patent teaches that the catalyst may be any basic nitrogen compound in which the nitrogen is contained in an aromatic 5- or 6-membered ring and which does not have any other functional groups (e.g. --NH.sub.2 or --OH groups) which are liable to form firm bonds with phosgene or carbonates under reaction conditions.